Re: [PATCH] x86/APIC: Remove workaround Pentium 3AP APIC_ESR erratum

[Javi Merino <javi.merino@xxxxxxxxx>]

On Wed, Nov 27, 2024 at 05:45:29PM +0000, Andrew Cooper wrote:
> On 27/11/2024 10:03 am, Javi Merino wrote:
> > On Tue, Nov 26, 2024 at 08:58:59PM +0000, Andrew Cooper wrote:
> >> The SDM instructs software to write 0 to ESR prior to reading it.  However,
> >> due to an original Pentium erratum, most logic skips the write based on 
> >> there
> >> being more than 3 LVTs; a stand-in to identify the Pentium.
> >>
> >> Xen, being 64bit, doesn't need compatibility for i586 processors.
> >>
> >> Introduce a new apic_read_esr() helper, quoting the SDM to explain why a
> >> function named apic_read_esr() has a write in it too.
> >>
> >> Use the new helper throughout apic.c and smpboot.c, which allows us to 
> >> remove
> >> some useless reads of APIC_LVR.  This in turn removes the external callers 
> >> of
> >> get_maxlvt(), so make it local to apic.c
> >>
> >> No practical change.
> >>
> >> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >> ---
> >> CC: Jan Beulich <JBeulich@xxxxxxxx>
> >> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >> CC: Javi Merino <javi.merino@xxxxxxxxx>
> >>
> >> Based on Javi's patch correcting error_interrupt()
> > Fair enough.  I was only looking at error_interrupt() and missed the
> > bigger picture. This patch is more comprehensive and this is very nice:
> >
> >> Bloat-o-meter reports:
> >>
> >>   add/remove: 0/1 grow/shrink: 0/3 up/down: 0/-269 (-269)
> >>   Function                                     old     new   delta
> >>   get_maxlvt                                    48       -     -48
> >>   __cpu_up                                    1465    1417     -48
> >>   clear_local_APIC                            1109    1050     -59
> >>   setup_local_APIC                             942     828    -114
> >> ---
> >>  xen/arch/x86/apic.c             | 29 ++++++++++-------------------
> >>  xen/arch/x86/include/asm/apic.h | 24 +++++++++++++++++++++++-
> >>  xen/arch/x86/smpboot.c          | 17 ++++-------------
> >>  3 files changed, 37 insertions(+), 33 deletions(-)
> > Reviewed-by: Javi Merino <javi.merino@xxxxxxxxx>
> 
> Thanks.  Are you happy for me to merge the two patches?

These changes represent a single logical change, so they should be in
one commit. Please merge the two patches.